Magnetron



Sept. 19, 1939. K. FRITZ 2,173,252

MAGNETRON Filed Nov. 12, 1936 2 Sheets-Sheet 1 INVENTOR KARL FRITZ B A ORNEY Sept. 19, 1939.

.llg 7a Al A4 A2 K. FRITZ MAGNETRON Filed NOV. 12, 1936 2 Sheets-Sheet 2 INVENTOR KARL FRITZ ATTORN EY Patented Sept. 19, 1939 PATENT OFFICE 2,173,252 MAGNETnoN Karl Fritz, Berlin, Gc

, assg-nor to Telemany funken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application November 12, 1936, Serial No. 110,439

In G

10 Claims.

The present invention relates to electron discharge devices, more particularly magnetrons with several anode segments, as well as circuit arrangements for producing high power when making use of these new tubes wherein reactive effects between the electrodes carrying alternating current (anode reaction) are avoided.

The power of a short-wave tube is limited essentially for two reasons: In the rst place, the source provided for electron emission (cathode) may not be able to furnish a sutciently large emission current and in the second place, the electrodes provided for the reception of emitted electrons may not be capable of absorbing the emission current coming from the cathode without the danger of destruction.

VThe cathode question is no longer of importance since the prior art has succeeded building high-emitting cathodes or so-called large-surface cathodes.

The principal difficulties are encountered in anode construction. The diameters of the anodes may not be increased beyond certain dimensions in practice for otherwise unreasonably high acceleration potentials must be applied for insuring a short transit time of the electrons. Moreover, the dimensions of the anodes in direction of the axis of electrode system cannot be chosen at will since an increase in the anode surface invariably results, with constant electrode distance, in an increase of the internal tube capacities which limits the range of the production of very short waves. In magnetron tubes an axial length as short as possible is desirable for the reason that the strong magnetic field extending through the discharge space must be homogeneous, and hence a considerable expenditure of magnet energizing power is required which must be increased with longer axial length. If the frontal electrodes (anodes) are increased in size for more favorable cooling conditions, the constructional'length of the tube is increased considerably in axial direction and therewith the magnetic resistance of the path to be traversed (air gap). Besides, the endeavor to draw the emission current to the frontal electrodes is only partlysuccessful. Not all electrons thrown off by cathode move in planes at right angle to cathode, many of these planes form in fact angles deviating from the right angle to the axis of system. These latter electrons move in a spiral line under the influence of the electric transverse field, whose axis is inclined to the axis of system, and they reach finally, even if not after the rst revolution, the current-carrying electrodes. The inuence of the electric transermany November 5,

(Cl. Z50-27.5)

verse eld on the electrodes varies greatly. It is a maximum at the ends of the discharge system and decreases strongly towards the center. Accordingly, the electrons emitted at the extremities of cathode pass directly to any end electrodes provided and thus do notl at all contribute to the generation of oscillations. On the other hand, the electronsemitted in the center of cathode are not iniiuenced at all for practical purposes by the electric transverse field.

'I'he raising of the efficiency in the usual magnetrons is limited for the reason that excessive alternating potentials between the oscillation electrodes interfere with an orderly course of the electrons so that the excitation of electrons is decreased. This detrimental anode reaction appears the more pronounced the greater the power output.

It is the principal object of my invention to provide a magnetron of increased power output and eiiciency.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figures la., b and c, are diagrammatic transverse sections of electron discharge tubes embodying my invention, Figures 2 to 4 inclusive are modifications of electron discharge tubes embodying my invention, Figures 5 and 6 are circuit arrangements using tubes embodying my invention, Figures 7a, 7b show further modifications of electron discharge tubes embodying my invention,

Figures 8, 9, 10a and 10b show other modifications and circuit arrangements embodying tubes made according to my invention.

By means of the present invention the problem of powerincrease in a tube is solved in a fully novel manner:

The electrodes carrying alternating current are not aiected by the waste heat produced through the imping'ement of the electrons. For this purpose a pick-up or collecting electrode is provided for the electrons, having the same distance from all points of the cathode with the result that its action extends uniformly over all electrons coming from cathode.

This new electrode shows pronounced screen electrode properties. It remains electrically neutral like a screen grid in a standard tube, in other words it carries no alternating potential with respect to cathode, in particular no alternating potential of the magnitude or frequency 55 of the oscillations produced. If it is impressed with a sufliciently high positive operating biasing potential, the resulting potential becomes trodes (anodes) enclosing the cathode is characterized in that the electrode group, producing the oscillations and consisting of the currentcarrying electrodes and the cathode, is enclosed by a single electrode, or several interconnected, electrodes (screen or pick-up electrodes).

An oscillating system may be used in the magnetron as long as it has perforated or slotted Ielectrodes thus presenting the possibility that the electrons may impinge on the neutral pickup electrode. The surface of the pick-up electrode is provided with cooling iins or the like for increasing heat radiation (natural cooling). The pick-up electrode may also be provided with arrangements for articial cooling by means of a liquid or gaseous medium. A-particularly advantageous construction results if the pick-up electrode is developed as a hollow cylinder, the other discharge electrodes being grouped concentrically within this cylinder. The pick-up electrodes form in this case at the same time a partial closure of the discharge space. The ends of the metallic cylinder are closed gas-tight with insulating members, particularly of ceramic material. These closing pieces are at the same time suitably made to participate in the support and centering of electrodes. In the case of use of this tube as a magnetron the electrodes are suitably made of non-magnetic material, thus preserving the homogeneity of the lines oi' force ux within the discharge space.

'Ihe novel tubes are to find their use principally in magnetron circuit arrangements for the purpose of insuring high power at short waves. As stated previously, the entire power loss (heat) is to be absorbed by the electrically neutral pick-up electrodes, while the oscillation energy is taken from the electrodes carrying alternating current only (anodes) and being freed of their load. For the reason that no alternating potential, at least none of the generated frequency, appears at the neutral pick-up electrode or electrodes, they can be developed in any desired manner and in particular can be grounded during operation. Complicated arrangements for insuring high ohmic or alternating resistances, such as would be required in water-cooled alternating current-carrying electrodes, are entirely superfluous in the present case, particularly when the pick-up electrode itself, or the correspondingpole of the biasing potential source is impressed with earth potential, similar to the arrangement usual in X-ray tubes.

In many cases where a reduction of the power loss at the oscillation electrode appears to be advisable, for instance in oscillations with magnetic elds of first magnitudewhere the over-all eiclency is poor, it may prove advantageous to use perforated screen electrodes and to dispose behind the screen electrodes having maximum positive potential the pick-up electrode proper with an average positive biasing potential that will retard the electrons and absorb the same with lower potential or velocity. Of equal importance as a suitable assembly of the discharge system is the choice of operating conditions. It is only the coordination of both that insures ideal separation of power loss and oscillation power, in other words their distribution over different types of electrodes. The operating conditions, that is electrode biasing potentials and magnetic eld must be chosen in the manner that an oscillation generation or amplification with respect to the oscillation electrodes as well as a catching of the electrons, which have already contributed to the oscillation generation, is insured by the pick-up electrodes. Experiments have shown that with correctly chosen operating conditions and corresponding tube construction no oscillation energy may be detected at the pick-up electrodes even if the latter are sub-divided and actually even if they are tuned to the produced frequency by means of suitable supplementary circuit elements. Even in the last-named case of resonance tuning in the pick-up electrode circuit no reactive iniluences of any kind are perceptible with respect to the interiorly disposed oscillation system for the electrons land in irregular sequence. The oscillation electrodes must, looking in a direction parallel to the axis of system, closely hug the paths of the revolving electrons, that is must have a course parallel to the latter so that the electrodes are hit to the least possible extent by the electrons. In View of above, preference will be given to oscillation electrodes with a cross-section in the form of a circular arc. v

By means of the introduction of the positive screen electrode, under the assumption of a suicient gain reciprocal through the perforated oscillation electrodes, the electric acceleration direct current eld may bechosen independent of the control alternating current fields in cylindre-symmetrical arrangement. This independence in 'the formation of the elds may be utilized to special advantage in a two-part oscillating system in the manner that the two oscillation electrodes are not disposed on a circle coaxial to the pick-up electrode, but are given a greater radius of curvature so that they are disposed in an ellipse-like curve at the center of which is located the cathode. By this arrangement the iniluence of the electric alternating current control fields on the cathode for the purpose of a sorting-out electron correct in phase (cathode separation) is increased, a possibility which may be of importance in particular in oscillations of the first order.

The alternating current carrying, positively .biased oscillation electrode (anodes) will not absorb. any direct current for all practical purposes especially in case of agrid-like construction. The discharge path co-ordinated vthereto has accordingly a very high resistance so that a control potential source connected in series therewith receives no or hardly any load. It is even possible to arrive at a condition where a negative direct current appears in the circuit of the oscillation electrodes and that is when the anodes have the property to throw off secondary electrons. These secondary electrons may likewise be put to good use.

Under normal conditions the fast primary electrons are accelerated by the oscillation electrode that is positive at the moment oi' exit and are curved or deflected by the magnetic ileld. 'I'hey then travel parallel to the short side of an oscillation electrode whose momentary potential is negative (leaving the biasing potential out of consideration). Electron m1 in traveling by, attracts through its iniluence a positive charge towards the electrode A1,'Fig. 1a giving a nega tive resistance eilect.

If it should happen that a primary electron reaches an oscillation electrode, it will land on van electrode whose momentary potential happens to be positive. This would have the result that additional further positive charge would be drawn to the positive electrode (positive resistance). In other Words, the electron lands at the wrong time with respect to phase and interferes with the excitation of oscillations. Fig. 1b indicates this case under the assumption that oscillation electrode A1 is in no way adapted to emit secondary electrons. The circuit arrangement is completed in Fig. 1b. 'I'he tube vessel R contains the cathode K and the positively biased 'pick-up or screen electrode N. The oscillating circuit is formed of inductance L and capacity C. A magnetic coil M induces a magnetic field between cathode and anode parallel to the cathode.

Fig. 1c illustrates a case by way of example Where even a landing electron may still contribute to the excitation of oscillations. Let m1 be the primary electron that iiies towards positive oscillation electrode A1 with the high velocity v1 but wrong in phase. It impinges thereon and releases a number of secondary electrons m2 with lesser speeds v2. In given cases the primary electron itself is reiiected (m1) by tangential incidence. 'Ihis results in that a negative charge is drawn to positive electrode A1 and the oscillation excitation is thus supported correct in phase. It is preferable for this reason in tubes according to invention to render the oscillation electrodes capable of secondary emission by means of suitable treatment of the surfaces or suitable material.

Figs. 2-3 show by way of example tube constructions or circuit arrangements in accordance with invention` for insuring high power output, particularly modulated oscillation output, in schematic manner.

Fig. 2 shows a section transverse to the axis of a concentrically arranged electrode system. Cathode K forms at the same time the axis of the discharge system. On a circle disposed coaxially with the cathode are arranged four anode segments A1, A2, A3 and A4, of equal size and displaced cyclically by 90. These anodes or oscillation electrodes may be connected together in the manner known in prior art and with a resonance system. -Behind these oscillation electrodes are disposed, likewise on a circle ci-axial with the cathode, four further pick-up or collecting electrodes N1, N11, Ns, N4 whichcover the corresponding slots between oscillation electrodes A. The pick-up electrodes are suitably directly connected electrically to each other by short-circuit connections Kv. The entire discharge system is enclosed in a hermetically sealed vessel R.

The phenomena inside the tube may be explained in this manner: the pick-up electrodes N furnish merely the electric direct current field required for acceleration of electrons while the oscillation electrodes (anodes) are coupled to the oscillating action of the electrons, for example capacitatively. The alternating potentials excited at the oscillation electrodes by inuence of the electrons that pass by, retroactively control the electron course.

In Fig. 3 are indicated the approximate paths ofthe electrons without these theoretical data limiting in any manner the mode of operation of the invention. One electron shall be selected out of the multitude. Its path shall be studied. It travels from the cathode toward oscillation electrode A1. The'diierence between the maximum diameter of the electron path and anode radius is d1. It turns back, travels to the vicinity of cathode and, at the proper moment, towards anode The approach to anode A2 is closer. The distance from anode' Aa is da. The action repeats itself until the radius of the path,

n say after passage past anode A4, becomes so great kunder the influence of picw-up electrode N, that the electron leaves `the oscillation space and flies to electron N as indicated by the curved arrow. In magnetrons with two oscillation electrodes it is preferable to construct these electrodes in perforated form, perhaps grid-like, so that the influence of electrode N is sumcientlystrong.

Fig. 4'shows a tube in transverse section, the foraminous oscillation electrodes A1', A2', A3 and A4' having meshor grid-like form. Optimum electric conditions are encountered if they consist of grid wires running at right angles to the cathode. Pick-up electrode N consists of a metallic cylinder N closed electrically up to the front sides and equipped with cooling ribs or fins Z. In order to vary the intensity of the eld produced by coil M, the source of supply V may be connected in series with the rheostat R1 and the coil M. The intensity of the field determines the radius of the path of the electrons around the cathode.

Fig. 5 shows the principle of a master-controlled amplifier tube provided with a multiple system. Both oscillating systems are enclosed by a pickup electrode N. K is the cathode. J1 and J2 are the electrodes of the inner system connected with an oscillating circuit St which for instance is excited bya control oscillator O. The amplied oscillation power is taken from perforated outer electrodes A1", A2" through an oscillating circuit H and brought to a receiver V. The case of course may exist where the inner system J1, J2 is excited to independent oscillations and where system A1", A2" is controlled by entrainment. Both oscillation systems are enclosed by the electrically neutral pick-up electrode N which absorbs as completely as possible the electrons after their work and thus lessens the anode retroaction.

Fig. 6 shows a modulation circuit arrangement where the modulation of the oscillations produced in the tube is accomplished by means of the pickup electrodes. 'I'he oscillation system, consisting of electrodes A1, A2, Aa, and A4 and resonance circuit H, operates in a self-excited circuit arrangement. 'I'he two parts N1' and N2' of pickup electrode are connected through capacities C11 inside or outside the tube. These capacities shall be dimensioned so that they present no appreciable resistance for the frequency of the produd oscillations, but oer a considerable resistance forthe modulation or regulation potentials. 'Ihe modulation potentials are impressed on pick-up electrodes N1 and N2' in push-pull arrangement by means of a modulation transformer M. The center terminal of the secondary of modulation transformer M is connected with the positive pole of the co-ordinated biasing potential source Un.

Hence, the source of the modulation oscillations is not connected in series with the discharge path comprising cathodes and pickup electrode, and cannot be loaded by the low resistance oi' this path. Cathode K is fed by a heating transformen T. Oscillation electrodes A1, Az, A1 and A4 are impressed with an average positive biasing potential Ug and pick-up electrodes N with the maximum positive biasing potential Un with respect to cathode.

It is of course also feasible, according to Figs. 7a, 7b, to divide the pick-up electrodes Ni', N2 not in sections parallel to axis of system, but by one or several sections at right angle to the axis of system and to connect these parts in suitable manner.

A tube similar to Fig. 6 is shown in Fig. 8. The difference consists in that the pick-up electrodes Ni' and N3' are bridged capacitatively by two further, exteriorly disposed pick-up electrodes Ni" and N2 and mutual capacities Ch with respect to the frequency of the produced oscillations. The maximum positive biasing potentials are in this case impressed on external electrodes N1", N1". If as shown, a modulation by means of electrodes N is done, it is preferable to impress asymmetrically one of the electrodes or electrode groups with an auxiliary biasing potential, for instance by means of a battery B, for preventing a doubling of the modulation frequency during modulation.

Fig. 9 shows a complete modulation circuit arrangement. The four oscillation electrodes A1, A2, A3, A4 work together with a resonance circuit H in a self-excited arrangement. This oscillation system is enclosed by fourperforated neutral electrodes N1', N2', N3', N4' arranged in a circle co-axial to cathode. Each of the two opposite neutral electrodes N1', and N3", N2 and N4 resp., are interconnected. The modulation potentials are impressed on these two groups in opposite phase. The biasing potential for all the neutral perforated electrodes is approximately the same and positive (Ua). Behind electrodes N' is disposed the pick-up electrode proper No", impressed with an average positive biasing potential Un" about of the size of oscillation electrode potential U.. The electrons are mainly accelerated by the maximum positive potential (Un') of electrodes N'. After passage through the perforated electrode N' they are retarded by the small p otential of electrode N" and land with smaller `speed on pick-up electrode proper No".

In Fig. 10a is shown a tube working in cooperation with a poorly radiating oscillation circuit. The mutual capacities of oscillation electrodes A1 and Az form a closed resonance circuit together with inductances Li which divide at points Cu in two parallel connected inductances La' and La" in the form of semi-cylindrical shells providing a closed housing around the electrodes.

The bridging capacities must be large comparedv to the mutual capacities of oscillation electrodes if they are not to be used for frequency regulation. On outer parts La' and La" are formed at points P', P potential nodes which carry no alternating potential with respect to earth (cathode) To this point are connected pick-up electrodes Ni' and N2". At one of these points'the pick-up electrode is impressed with the positive biasing potential and at another point the cathode feed line is introduced in the interior of the discharge system. The pick-up electrodes are connected with the exteriorly disposed oscillation inductances La. and La" a great part of the oscillation circuit participating in the radiation oi' the waste heat.

The principle of the circuit arrangement is indicated in Fig. 10b. A particularly favorable embodiment results when the oscillation circuit is developed in form of a globe. For introduction of the electrode leads, holes must be provided at points p' and Cu.

It appears essential to once more emphasize at this point that the oscillation system disposed inside the electrically neutral pick-up electrode (N) may be developed in any desired manner. It may be constructed as a master control system with two built-in electrode systems having different distances from the cathode. It may even consist of a cathode and cylindrical anode, only, assuming that the anode is of gridor mesh-like form to allow passage of theelectrons. Auxiliary electrodes for modulation, regulation, control, etc. may be used in line with all possible and usual schemes for magnetrons and variants. Thus, a modulation with the air of oscillation electrodes (anodes) in straight or push-pull arrangement is possible or a combined modulation. Nothing prevents the arrangement of disk-like electrodes at the front side of the discharge sys. tems using thesame for excitation of oscillations and/or modulation.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specic application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope o f my invention as set forth in the appended claims.

I claim:

1. An electron discharge device having an envelope containing a straight thermionic cathode and a plurality of anodes surrounding said cathode, and a collecting electrode outside of said anodes for receiving electrons from said cathode, and means for inducing a stable magnetic field between said cathode and anodes parallel to said cathode. Y

2. An electron discharge device having a straight thermionic cathode and a plurality of anode segments surrounding and parallel to the cathode, a second electrode surrounding said cathode and said anodes for receiving electrons from the cathode and means for inducing a magnetic field between said cathode and anode segments parallel to said cathode.

3. An electron discharge device having an envelope containing a straight thermionic cathode and a plurality of anode segments surrounding said cathode, said anode segments being parallel to the cathode and arranged in oppositely disposed pairs at different distances from the cathode, and an electrode surrounding said cathode and anode segments, and means for inducing a magnetic field between said cathode and anode segments parallel to said cathode.

4. An electron discharge device having an envelope containing a straight thermionic cathode and a plurality of foraminous anode segments surrounding said cathode and a cylindrical electrode surrounding said cathode and anodes, and means for inducing a magnetic held between said cathode and anode segments.

5. An electron discharge device having an envelope containing a straight thermionic cathode and a plurality of foraminous anode segments surrounding said cathode and a solid cylindrical electrode surrounding said cathode and anodes and provide with radially extending cooling ns, and means for inducing a magnetic eld between said cathode and foraminous anode segments.

6. Anelectron discharge device having an envelope containing a straight thermionic cathode and a plurality of anodes surrounding said cathode, and a collecting electrode outside of said anodes for receiving electrons from said cathode, and means for inducing a magnetic field between said cathode and anodes parallel to said cathode, and an oscillating circuit in the form of a closed screen housing carrying the collecting electrode at the electrically neutral points on said oscillating circuit.

7. An electron discharge device having an envelope containing a straight thermionic cathode and a plurality of anodes surrounding said cathode, and a collecting electrode of non-ferromagneticmaterial outside of said anodes for receiving electrons from said cathode, and means for inducing a stable magnetic eld between said cathode and anodes parallel to said cathode.

8. An electron discharge device having a straight thermionic cathode and a plurality of anode segments surrounding said cathode, said anode segments being perforated and enclosed by a solid sheet metal collecting electrode, and means for inducing a magnetic iield between said cathode and said anode segments. 9. An electron discharge device having a envelope containing a straight thermionic cathode and a plurality of anodes surrounding said cathode, and a collecting electrode outside of said anodes for receiving electrons from said cathode, and means for inducing a stable magnetic field between said cathode and anodes.

parallel to said cathode, and means for adjusting the magnetic eld so that all of the electrons are received by the collecting electrode.

10. An electron discharge device having an envelope containing a straight thermionic cathode and a plurality of anodes surrounding said cathode, and a collecting electrode outside of said anodes for receiving electrons from said cathode, and means for inducing a magnetic iield between said cathode and anodes parallel to said cathode, said collecting electrode being subdivided into sections at right angles to the axis of the cathode and electrically insulated from each other.

KARL FRITZ. 

